To generate a robust and effective immune response, T cells must integrate pathogen-derived and micro- environmental signals; these include availability of nutrients and oxygen. Together these signals regulate the metabolic changes necessary for the dramatic expansion of effector T cells armed to eliminate pathogens. We have found that a specific metabolic response pathway controls T cell immunity, and will identify the signaling and physiological parameters that link the metabolic activity of T cells during their response to pathogen with their differentiation and function. ) PUBLIC HEALTH RELEVANCE: The CD8+ T cell immune response is essential for the clearance of many intracellular pathogens including viruses, bacteria and protozoan parasites. Infection initiates a program of differentiation by CD8+ T cells resulting in dramatic proliferation and differentiation into effector cells, which access tissues to induce apoptosis of infected cells. Thus, cytotoxic CD8+ T cells must balance the metabolic requirements of expansion and survival with the limiting nutrient and oxygen availability of infected tissues. During the resolution of infection, a long-lived memory population emerges to provide protection from reinfection. While T cell activation induces a profound metabolic shift to glycolysis, how metabolic activity influences the contraction of effector cells and the transition to memory has been until recently largely unexplored. Several studies have revealed that a metabolic switch from glycolytic to fatty acid metabolism is important for the development of long-lived CD8+ memory cells. These results suggest metabolism may fundamentally underpin cell fate decisions leading to the generation of adaptive immunological memory. However, how the function and differentiation of effector and memory CD8+ T cells are linked to metabolic activity, which is influenced by the microenvironment during infection, is unknown. Our proposal focuses on the von Hippel-Lindau/Hypoxia-inducible Factor (VHL/HIF) pathway, which controls the transcriptionally-induced metabolic responses to hypoxia, to pose questions about the signaling and physiological parameters that link the metabolic requirements of T cells to their function and differentiation. Specifically, we will: 1) Establish the importance of the VHL/HIF pathway for T cell homeostasis, immunity, and memory formation. We hypothesize that metabolic shifts regulated by VHL play an important role in T cell survival, responses to infection, and memory formation. Using specific deletion of VHL in mature T cells, we will examine T cell homeostasis, responses to primary and secondary infections, and the magnitude, kinetics, and quality of memory formation. 2) Define the molecular pathways underpinning VHL modulation of T cell immunity. We hypothesize that VHL modulates T cell immunity by attenuating HIF activity. We will study the immune response by T cells with individual and/or compound HIF11, HIF21 and VHL mutations. Global gene-expression analysis will be used to determine the molecular targets of the VHL/HIF pathway that influence CD8+ T cell function and effector/memory formation. 3) Identify the physiologic signals regulating HIF activity during T cell responses. We will explore how hypoxia, TCR-stimulation and exposure to cytokines together regulate HIF activity. A new mouse model that allows the monitoring of HIF activity by individual, live cells during an in vivo immune response to infection will be generated and used to understand how T cells integrate multiple signals to regulate activity of the VHL/HIF pathway in systemic and tissue-specific T cell immune responses. Ultimately, these studies will provide a comprehensive understanding of the role of the VHL/HIF pathway in T cell immunity. )